Arrangements for magnetic field sensors that act as tooth detectors

Abstract

A magnetic field sensor for sensing motion of a ferromagnetic object comprises a substrate. The substrate includes first and second major surfaces, each having a width dimension and a length dimension. The magnetic field sensor further comprises a magnet. The magnet includes a first major surface proximate to the substrate, the first major surface of the magnet heaving a width and a length, and a second major surface. The magnetic field sensor further includes first and second magnetic field sensing dements. The first magnetic field sensing element and the second magnetic field sensing element are positioned beyond respective ends of the width of the magnet. The second magnetic field sensing element is substantially farther from the ferromagnetic object than the first magnetic field sensing element. A line passing through the first and second magnetic field sensing elements is perpendicular to the magnet axis.

What is claimed is: 
     
       1. A magnetic field sensor for sensing motion of a ferromagnetic object, comprising:
 a substrate, comprising:
 a first major surface, wherein a first dimension across the first major surface of the substrate defines a width dimension of the substrate and a second dimension across the first major surface of the substrate perpendicular to the width dimension defines a length dimension of the substrate; 
 first and second substrate edges at ends of the width dimension of the substrate; and 
 a second major surface parallel to the first major surface, wherein the magnetic field sensor further comprises: 
 
 a magnet, comprising:
 a first major surface proximate to the substrate and substantially parallel to the first major surface of the substrate, wherein a first dimension across the first major surface of the magnet defines a width dimension of the magnet and a second dimension across the first major surface of the magnet perpendicular to the width dimension defines a length dimension of the magnet; 
 a second major surface distal from the substrate and parallel to the first major surface of the magnet; and 
 a magnet axis perpendicular to the first and second major surfaces of the magnet and centered within the width dimension and length dimension of the magnet, wherein the magnetic field sensor further comprises: 
 
 a first magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a first magnetic field signal, wherein the first magnetic field sensing element comprises a center; and 
 a second magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a second magnetic field signal, wherein the second magnetic field sensing element comprises a center, wherein the center of the first magnetic field sensing element and the center of the second magnetic field sensing element are the same distance from the first major surface of the magnet, wherein the first and second magnetic field sensing elements are disposed on opposite sides of the magnet axis, wherein the first magnetic field sensing element is disposed proximate to the ferromagnetic object and beyond the magnet such that a first line perpendicular to the substrate and intersecting the center of the first magnetic field sensing element does not intersect the magnet, wherein a line passing through the first and second magnetic field sensing elements intersects the ferromagnetic object, wherein the line passing through the first and second magnetic field sensing elements is parallel to the width dimension of the substrate and parallel to the width dimension of the magnet, wherein the second magnetic field sensing element is substantially farther from the ferromagnetic object than the first magnetic field sensing element, resulting in the first magnetic field sensing element being substantially more responsive to the motion of the ferromagnetic object than the second magnetic field sensing element, wherein the magnet is offset from the line passing through the first and second magnetic field sensing elements in a direction perpendicular to the line passing through the first and second magnetic field sensing elements, and wherein the line passing through the first and second magnetic field sensing elements is perpendicular to the magnet axis. 
 
     
     
       2. The magnetic field sensor of  claim 1 , wherein the magnet comprises magnetic particles molded within a mold compound. 
     
     
       3. The magnetic field sensor of  claim 1 , further comprising an electronic circuit disposed upon the substrate, coupled to receive the first and second magnetic field signals, and configured to sum the first and second magnetic field signals. 
     
     
       4. The magnetic field sensor of  claim 1 , further comprising:
 a leadframe over which the substrate is disposed, the leadframe comprising a plurality of leads; 
 a molded body encapsulating the substrate and selected parts of the leadframe; and 
 one or more passive electronic components disposed within the molded body apart from the substrate and electrically coupled to at least two of the plurality of leads. 
 
     
     
       5. The magnetic field sensor of  claim 1 , wherein the substrate further comprises a substrate center axis perpendicular to the first and second major surface of the substrate and centered within the width dimension and length dimension of the substrate; wherein the magnet axis is substantially parallel to and proximate to the substrate center axis. 
     
     
       6. The magnetic field sensor of  claim 1 , wherein the first magnetic field sensing element is responsive to movement of the ferromagnetic object, and wherein the second magnetic field sensing element is substantially unresponsive to the movement of the ferromagnetic object. 
     
     
       7. The magnetic field sensor of  claim 1 , wherein a first distance between the center of the first magnetic field sensing element and a first end of the width dimension of the magnet is substantially smaller than a second distance between the first end of the width dimension of the magnet and the magnet axis. 
     
     
       8. The magnetic field sensor of  claim 7 , wherein a third distance between the center of the second magnetic field sensing element and a second end of the width dimension of the magnet is substantially smaller than a fourth distance between the second end of the width dimension of the magnet and the magnet axis. 
     
     
       9. The magnetic field sensor of  claim 7 , wherein a third distance between the center of the second magnetic field sensing element and a second end of the width dimension of the magnet is substantially larger than a fourth distance between the center of the second magnetic field sensing element and the magnet axis. 
     
     
       10. The magnetic field sensor of  claim 1 , further comprising at least one amplifier disposed upon the substrate electrically coupled to the first and second magnetic field sensing elements. 
     
     
       11. The magnetic field sensor of  claim 1 , wherein the second magnetic field sensing element is disposed distal from the ferromagnetic object and beyond the magnet such that a second line perpendicular to the substrate and intersecting the center of the second magnetic field sensing element does not intersect the magnet. 
     
     
       12. The magnetic field sensor of  claim 1 , wherein the second magnetic field sensing element is disposed distal from the ferromagnetic object and at a position such that a second line perpendicular to the substrate and intersecting the center of the second magnetic field sensing element intersects the magnet. 
     
     
       13. The magnetic field sensor of  claim 1 , wherein the magnetic field sensor further comprises: an electronic circuit disposed on or within the substrate and electrically coupled to the first and second magnetic field sensing elements. 
     
     
       14. The magnetic field sensor of  claim 1 , wherein the first magnetic field sensing element is selected from among a respective plurality of magnetic field sensing elements disposed upon the first major surface or the second major surface of the substrate, the selection of the first magnetic field sensing element based upon a desired accuracy characteristic of the magnetic field sensor, and other ones of the plurality of magnetic field sensing elements are inactive, and wherein the second magnetic field sensing element is not selected from any group of magnetic field sensing elements, wherein the first magnetic field sensing element and the second magnetic field sensing element are not coupled together in a bridge arrangement. 
     
     
       15. The magnetic field sensor of  claim 1 , wherein the first magnetic field sensing element is selected from among a respective plurality of magnetic field sensing elements disposed upon the first major surface or the second major surface of the substrate, the selection of the first magnetic field sensing element based upon a desired accuracy characteristic of the magnetic field sensor, and other ones of the plurality of magnetic field sensing elements are inactive, and wherein the second magnetic field sensing element is not selected from any group of magnetic field sensing elements. 
     
     
       16. The magnetic field sensor of  claim 1 , wherein the first magnetic field sensing element and the second magnetic field sensing element are not coupled together in a bridge arrangement. 
     
     
       17. The magnetic field sensor of  claim 1 , wherein the first and second magnetic field sensing elements are planar Hall effect elements. 
     
     
       18. A magnetic field sensor for sensing motion of a ferromagnetic object, comprising:
 a substrate, comprising:
 a first major surface, wherein a first dimension across the first major surface of the substrate defines a width dimension of the substrate and a second dimension across the first major surface of the substrate perpendicular to the width dimension defines a length dimension of the substrate; 
 first and second substrate edges at ends of the width dimension of the substrate; and 
 a second major surface parallel to the first major surface, wherein the magnetic field sensor further comprises: 
 
 a magnet, comprising:
 a first major surface proximate to the substrate and substantially parallel to the first major surface of the substrate, wherein a first dimension across the first major surface of the magnet defines a width dimension of the magnet and a second dimension across the first major surface of the magnet perpendicular to the width dimension defines a length dimension of the magnet; 
 a second major surface distal from the substrate and parallel to the first major surface of the magnet; and 
 a magnet axis perpendicular to the first and second major surfaces of the magnet and centered within the width dimension and length dimension of the magnet, wherein the magnetic field sensor further comprises: 
 
 a first magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a first magnetic field signal, wherein the first magnetic field sensing element comprises a center; and 
 a second magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a second magnetic field signal, wherein the second magnetic field sensing element comprises a center, wherein the center of the first magnetic field sensing element and the center of the second magnetic field sensing element are the same distance from the first major surface of the magnet, wherein the first and second magnetic field sensing elements are disposed on opposite sides of the magnet axis, wherein the first magnetic field sensing element is disposed proximate to the ferromagnetic object and beyond the magnet such that a first line perpendicular to the substrate and intersecting the center of the first magnetic field sensing element does not intersect the magnet, wherein a line passing through the first and second magnetic field sensing elements intersects the ferromagnetic object, wherein the line passing through the first and second magnetic field sensing elements is parallel to the width dimension of the substrate and parallel to the width dimension of the magnet, wherein the second magnetic field sensing element is substantially farther from the ferromagnetic object than the first magnetic field sensing element, resulting in the first magnetic field sensing element being substantially more responsive to the motion of the ferromagnetic object than the second magnetic field sensing element, wherein the magnet is offset from the line passing through the first and second magnetic field sensing elements in a direction perpendicular to the line passing through the first and second magnetic field sensing elements, wherein the line passing through the first and second magnetic field sensing elements is perpendicular to the magnet axis, and wherein the magnetic field sensor is operable to generate an output signal having a value that can distinguish between a tooth and a valley of the ferromagnetic object when the ferromagnetic object is moving and when the ferromagnetic object is not moving. 
 
     
     
       19. The magnetic field sensor of  claim 18 , wherein the magnet comprises magnetic particles molded within a mold compound. 
     
     
       20. The magnetic field sensor of  claim 18 , further comprising an electronic circuit disposed upon the substrate, coupled to receive the first and second magnetic field signals, and configured to sum the first and second magnetic field signals. 
     
     
       21. The magnetic field sensor of  claim 18 , further comprising:
 a leadframe over which the substrate is disposed, the leadframe comprising a plurality of leads; 
 a molded body encapsulating the substrate and selected parts of the leadframe; and 
 one or more passive electronic components disposed within the molded body apart from the substrate and electrically coupled to at least two of the plurality of leads. 
 
     
     
       22. The magnetic field sensor of  claim 18 , wherein the first magnetic field sensing element is selected from among a first plurality of magnetic field sensing elements disposed upon the first surface of the substrate, the selection of the first magnetic field sensing element based upon a desired behavior of the magnetic field sensor and other ones of the first plurality of magnetic field sensing elements are inactive, and the second magnetic field sensing element is selected from among a second plurality of magnetic field sensing elements disposed upon the first major surface or the second major surface of the substrate, the selection of the second magnetic field sensing element based upon the desired behavior of the magnetic field sensor and other ones of the second plurality of magnetic field sensing elements are inactive. 
     
     
       23. The magnetic field sensor of  claim 18 , wherein the substrate further comprises a substrate center axis perpendicular to the first and second major surface of the substrate and centered within the width dimension and length dimension of the substrate; wherein the magnet axis is substantially parallel to and proximate to the substrate center axis. 
     
     
       24. The magnetic field sensor of  claim 18 , wherein the first magnetic field sensing element is responsive to movement of the ferromagnetic object, and wherein the second magnetic field sensing element is substantially unresponsive to the movement of the ferromagnetic object. 
     
     
       25. The magnetic field sensor of  claim 18 , wherein a first distance between the center of the first magnetic field sensing element and a first end of the width dimension of the magnet is substantially smaller than a second distance between the first end of the width dimension of the magnet and the magnet axis. 
     
     
       26. The magnetic field sensor of  claim 25 , wherein a third distance between the center of the second magnetic field sensing element and a second end of the width dimension of the magnet is substantially smaller than a fourth distance between the second end of the width dimension of the magnet and the magnet axis. 
     
     
       27. The magnetic field sensor of  claim 8 , wherein a third distance between the center of the second magnetic field sensing element and a second end of the width dimension of the magnet is substantially larger than a fourth distance between the center of the second magnetic field sensing element and the magnet axis. 
     
     
       28. The magnetic field sensor of  claim 18 , wherein the first magnetic field sensing element is selected from among a plurality of magnetic field sensing elements disposed upon the first major surface or the second major surface of the substrate, the selection of the first magnetic field sensing element based upon a desired accuracy characteristic of the magnetic field sensor, and other ones of the plurality of magnetic field sensing elements are inactive. 
     
     
       29. The magnetic field sensor of  claim 18 , further comprising at least one amplifier disposed upon the substrate between and electrically coupled to the first and second magnetic field sensing elements. 
     
     
       30. The magnetic field sensor of  claim 18 , wherein the second magnetic field sensing element is disposed distal from the ferromagnetic object and beyond the magnet such that a second line perpendicular to the substrate and intersecting the center of the second magnetic field sensing element does not intersect the magnet. 
     
     
       31. The magnetic field sensor of  claim 18 , wherein the second magnetic field sensing element is disposed distal from the ferromagnetic object and at a position such that a second line perpendicular to the substrate and intersecting the center of the second magnetic field sensing element intersects the magnet. 
     
     
       32. The magnetic field sensor of  claim 18 , wherein the magnetic field sensor further comprises: an electronic circuit disposed on or within the substrate and electrically coupled to the first and second magnetic field sensing elements. 
     
     
       33. The magnetic field sensor of  claim 18 , wherein the first magnetic field sensing element and the second magnetic field sensing element are not coupled together in a bridge arrangement. 
     
     
       34. The magnetic field sensor of  claim 18 , wherein the first and second magnetic field sensing elements are planar Hall effect elements.